Bit of a messy patch data wise but I think I got most of Rek'Sai (also to whoever moved the string table, you got me, -2 minutes of my life).
Now let's talk about the Malignance change (or rather, non-change, as the tooltip merely got updated to convey its live functionality).
Malignance is currently being told to never trigger on damage that contains the BasicAttack tag. This is currently preventing the item from working with Warwick ult (who does actually have a serviceable AP build) and Viego ult (much less serviceable but will become useful for this discussion).
Both of these spells are tagged as both BasicAttack and ActiveSpell against their primary target, with Viego being simply ActiveSpell against his secondary targets. This means that both spells will normally apply all other spell effects to the target without issue. Malignance instead ignores them both purely for having the BasicAttack tag. However, in Viego's case, if you happen to have more than one target, you will be able to trigger Malignance, since secondary targets are not BasicAttack.
This appears to actually be an attempt to exclude specifically pet attacks such as Yorick's Maiden, Ivern's Daisy, and Annie's Tibbers. However even this is not very consistent, as Annie is able to trigger it anyways from the Tibbers aura, so the exclusion for him is irrelevant (if the concern was being ran down by pets spamming Malignance aoes, well he's already doing exactly that). Meanwhile Daisy is able to trigger it for her knockup attack, because that counts as ActiveSpell and not BasicAttack. Maiden is unable to trigger by any means.
Furthermore, Shaco ult's boxes are allowed to trigger, despite being pet attacks originating from his ult slot, purely because they are not tagged as BasicAttack.
Katarina ult is also allowed to trigger despite applying onhits, because it is not tagged as BasicAttack.
And now today, Riot has seemingly decided all of this is desirable behavior and has now written the bug into the tooltip.
Overall the entire thing seems misguided. If they want to ignore pets, then they could just check for the Pet tag instead, and add the tag to Tibbers aura and Daisy knockup. This would then also catch Shaco boxes. Or, they could accept that pets can already largely apply Malignance anyways, and drop the entire BasicAttack exclusion outright.
Currently Warwick and Viego (and more importantly, any possible future champions that might have a BasicAttack ult) are being excluded purely as collateral from an (unsuccessful) attempt to exclude pets. It's not good enough to simply just say "well it already works like this, no point in changing it so now I'm saying it was actually intentional the whole time to prevent Warwick from using the item".
Lastly, I don't actually give any fucks about AP Warwick, I just don't like that Riot often uses a mentality like this one to escape fixing trivial things because "well it's working as implemented" without actually bothering to consider whether that implementation is holistically desirable in the first place and whether better and simple alternatives readily exist, so I'm calling it out.